1. Field Of The Invention
The present invention relates to processors permitting a telephone subscriber having a television set to communicate with a computer, the keyboard telephone set of the subscriber serving as a terminal for transmitting and receiving digital signals and the television set serving as a display console.
No modification is required either in the telephone set or in the television set and the processor is connected between terminals for an additional earpiece on the telephone set and the aerial socket of the television set. It is also possible to connect the processor to an acoustic coupler to which the user applies the telephone set. The transition from the reception of a television channel to the displaying of computer answers takes place through a channel switch in the television set.
2. Description of the Prior Art
The conventional multi-frequency call keyboard telephone sets emit two audio frequencies when a call key is depressed. The two emitted frequencies are a lower frequency selected from the group comprising the frequencies 697, 770, 852, and 941 Hz, and a high frequency selected from the group comprising the frequencies 1209, 1336, and 1477 Hz. The computer is interrogated through keys of the keyboard which have two meanings, i.e. a digital meaning and a functional meaning as will be explained below.
The computer reply is returned as a frequency modulation, the frequency of 1650 Hz representing logic level one and the frequency of 1850 Hz representing logic level zero. Words representing the characters comprise seven code bits, a parity bit, a start bit and two stop bits. In the case of a transmission speed of 200 bits per second, the modulation spectrum ranges between 1500 and 2000 Hz. The seven-bit code words representing the characters are translated by the processor into alpha-numeric characters of a matrix having 35 points stored in a read-only memory.